--- a/usr/gen_initramfs.sh
+++ b/usr/gen_initramfs.sh
@@ -239,7 +239,7 @@ done
 # we are careful to delete tmp files
 timestamp=
 if test -n "$KBUILD_BUILD_TIMESTAMP"; then
-	timestamp="$(date -d"$KBUILD_BUILD_TIMESTAMP" +%s || :)"
+	timestamp="$(date -j -f "%a %b %e %H:%M:%S UTC %Y" "$KBUILD_BUILD_TIMESTAMP" +%s || :)"
 	if test -n "$timestamp"; then
 		timestamp="-t $timestamp"
 	fi
